In producing well logging measurements for purposes of recording, a logging tool containing one or more exploring devices is lowered into a wellbore drilled into the earth for measuring various properties of the subsurface earth formations adjacent the wellbore. Such measurements are of considerable value in determining the presence and depth of hydrocarbon bearing zones that may exist in the subsurface earth formations. There are presently in use a variety of galvanometer recorders capable of providing satisfactory well logs or recordings representative of most types of data derived from a wellbore. Some of these galvanometer recorders are specifically useful for recording a large number of different well logging data signals at one time. Examples of such recorders are described in: (1) U.S. Pat. No. 3,449,755 which issued to G. L. Samodai, et al. on June 10, 1969; (2) U.S. Pat. No. 3,488,661 which issued to D. R. Tanguy on Jan. 6, 1970; and (3) U.S. Pat. No. 3,634,865 which issued to C. O. Schafer on Jan. 11, 1972. In addition, a particularly suitable CRT recorder for recording a multiplicity of well logging measurements is described in copending application Ser. No. 15,790 filed by J. W. Elliott on Mar. 2, 1970. However, not withstanding the versatility of the recorders described in the above-mentioned patents, there are certain types of well logging data which are most advantageously displayed on a log or recording in a manner which requires even more specific methods and apparatus for generating the desired display. To date, there have been many attempts to provide the necessary recording methods and apparatus to generate these unique displays.
For example, special purpose recorders have been developed for providing sonic or acoustic logs in special forms which present some unusual recording problems. A typical sonic or acoustic logging tool provides a transmitting transducer for repetitively transmitting an acoustic burst of energy into the earth formations adjoining a wellbore in response to a recurrent firing pulse. A receiving transducer then converts the received acoustical energy into electrical signals for transmission to the surface of the earth for recording. In certain types of such sonic logging systems only the travel time .DELTA.t of the sonic energy in the formation is recorded. However, it has been recognized that valuable additional information about the earth formation may be obtained by recording and analysing the complete waveform. Therefore, it is of increasing importance that all subsequent arriving waves as well as the recurrent firing pulse or a pulse correlated with the recurrent firing pulse be recorded along with the first arriving wave or impulse.
One technique for recording the waveforms comprising such acoustic or sonic logging signals is shown in U.S. Pat. No. 3,488,658 granted to Dennis R. Tanguy on Jan. 6, 1970, wherein a glow modulator tube is utilized in conjunction with a rotating mirror to sweep an intensity modulated light beam across a recording medium. The light beam is swept at the repetition rate of the recurrent firing pulse used to drive the transmitting transducer.
Another logging apparatus used in acoustic logging is described in U.S. Pat. No. 3,302,165 granted to T. O. Anderson, et al. on Jan. 31, 1967. The Anderson patent describes a method for obtaining so-called "variable-density logs" by utilizing an oscilloscope-camera combination. The intensity of the oscilloscope beam is varied in accordance with variations in the amplitude of the received well logging signal as the beam sweeps across the cathode-ray tube screen. Each successive sweep of the beam is representative of a different level in the wellbore.
In similar apparatus described in the U.S. Pat. No. 3,402,388 granted to Robert L. Tucker on Sept. 17, 1968, the beam intensity, during a predetermined number of successive sweeps, is modulated as in the Anderson patent. However, during the sweep following this predetermined number of intensity-modulated, successive sweeps, the vertical position of the beam is modulated instead of the beam intensity. After completing the sweep wherein the vertical position is modulated, the beam is again intensity-modulated for the predetermined number of sweeps. The Tucker technique results in a variable density log being produced similar to that produced by the Anderson apparatus, but which also includes a "signature line" (the vertical position modulated trace) at spaced intervals along the log.
In another example, so-called "televiewer" logging apparatus (such as described in U.S. Pat. No. 3,502,169 granted to J. E. Chapman on Mar. 24, 1970 and copending application Ser. No. 827,799 also filed by J. E. Chapman on May 26, 1969) generates and displays data in such a manner that a picture of the wellbore wall is provided. This "televiewer" apparatus rotates a directional sonic transducer so as to continuously scan the circumference of a wellbore wall by alternately transmitting and receiving successive bursts of acoustic energy to provide the composite picture of the wellbore wall. To provide a directional reference, recurrent azimuthal signals are also transmitted to the surface of the earth as they occur, so that the resulting recorded log can be referenced to the azimuthal direction. The surface recording apparatus displays this information in a manner similar to that for displaying the sonic or acoustic logs.
Heretofore, therefore, the logs provided by the recording apparatus representative of various types of received sonic signals have been limited to sonic-.DELTA. t, waveform reproduction and variations of variable density desplays. Such logs have not been completely satisfactory as such logs are often very difficult to interpret.
Therefore, to provide well logs which lend themselves to easy interpretation, it is an object of this invention to provide new and unique methods and apparatus for providing acoustic and "televiewer" logs having an easily interpretable "three-dimensional" visual appearance which is pleasant to the eye.
Still another example of data which requires unusual methods and apparatus for the most advantageous display is that used for providing arrow-plots or vectors. Arrow-plot logs are presently used to provide information concerning: (1) the magnitude and direction of the inclination of a wellbore; and (2) the magnitude and direction of the dip or inclination of earth formations surrounding a wellbore relative to true vertical. It is of great practical importance to have information concerning the position and orientation of the wellbore along its length with respect to the starting point thereof on the earth's surface. This information is useful, for example, to insure that the borehole remains within a predetermined land area measured at the surface. It is also of great practical importance to have information concerning the position of subsurface earth formations in areas possibly containing or known to contain oil and gas bearing formations. This information is useful in that, among other things, it may aid in locating sizeable deposits of oil and gas trapped by faults or subsurface layers of slipped strata. It is also desirable since knowledge of subsurface faults or slipped strata may allow the oil field to be developed most efficiently. For example, the simple placement of wells can radically effect both the maximum rate of production and the ultimate recovery from a single oil reservoir.
Arrow-plot logs providing such information concerning the inclination of wellbores or formations have typically been provided manually from tabulated data. Although, in some instances the arrow-plots have been produced automatically by an "X"-"Y" plotter or a special purpose recorder. However, such methods have typically been time consuming and costly.
Therefore, it is another object of this invention to provide new and unique methods and apparatus for generating logs comprised of "arrows" or vectors representative of data corresponding to the magnitude and direction of the inclination of a wellbore or the magnitude and direction of the inclination of earth formations adjacent a wellbore.
With present logging techniques, it is likely that data from a multiplicity of downhole investigating devices of different types derived from one logging apparatus during one run or from multiple logging tools run at separate times might be combined for recording. In such cases, it may be desirable to present all of the different logs resulting from these various investigating devices on the same recording medium. However, if the combination of logs to be presented on one recording medium includes at least one of the so-called "standard" or amplitude versus depth logs such as sonic-.DELTA. t or the like along with one of the "unusual" logs such as those produced by the methods and apparatus of this invention, some difficult problems arise. For example, if a CRT recorder is to be used it may be highly desirable that different sweep rates be used for the standard and unusual logs. In addition, if a single sweep of the CRT electron beam is used to produce both a standard and an unusual log such as a realtime recording of a sonic waveform, the recorder must be able to record the standard log without missing any traces and yet be ready to record the unsynchronized realtime waveform whenever it occurs. It is necessary, of course, to record the waveform whenever it occurs, unless extensive memory is provided, as the waveform will be lost and cannot be recovered. Therefore, it is a still further object of this invention to provide new and novel methods and apparatus for generating standard logs in combination with one or more of the unusual logs such as sonic waveforms, variable density, televiewer or "inclination" all on the same recording medium.
As was mentioned heretofore, it is not unusual that data from a multiplicity of downhole investigating devices be available for recording at the same time, and that it is often desirable that at least some of the data be combined and recorded on a single recording medium. However, the width of a recording medium is limited (typically, commercial logs are recorded on a medium approximately eight inches in width), and if there are a great number of different types of data that should be recorded at the same time, the amount of recording medium space available for each log or curve will be severely limited. Such space limitations normally adversely affect the ease of interpretation of a log and often also affect the resolution of the many curves on the log. For example, most of the unusual logs will require a large portion of a single recording medium (typically, half). Now, if there is also a large number of standard logs to be recorded, only the unused half of the recording medium is available for this large number of standard logs. This means that each of these standard logs may either be confined to a very small track on the single recording medium which will severely limit the resolution of the logs, or the logs will have a mid-point in a particular track and be allowed wide excursions into and across other tracks. Repeated, multiple and far-reaching excursions of logs into other tracks is often very confusing and makes the task of interpreting the data very difficult. Therefore, to provide excellent resolution of all the data needed to be recorded and at the same time still provide necessary side-by-side combination logs of that data where such side-by-side curves are preferred, it is desirable that more space on a recording medium be available for each of the logs or curves. Even when there is not a large number of different data to be recorded at the same time, it is not unusual that a particular log or portion of a log be of greater interest than the rest. If such interest is present, it might be advantageous that the log be recorded with an expanded depth scale, or that the data be allowed to range over a large portion of the available width of the recording medium to thereby provide greater resolution and ease of interpretation.
Therefore, to provide a greater area of recording medium available for each track or log to be recorded, one embodiment of the present invention includes at least two recording mediums operably arranged with a single CRT such that each recording medium records available data at substantially the same time.